What is the best steps to snap the torus to floor level?
Align Objects [space menu search]

The Torus was selected. Next yellow floor last to become the active object.




The figure on the right shows two objects not yet aligned.  Torus and Plane.
The figure on the  left show two objects aligned.
The Tool Shelf shows the parameters used in this example ... Negative Sides, Active, Align Z.  The plane has the negative side and positive side in the same location .... plane.


Other options show in the Tool Shelf. Selection, 3D Cursor, Scene Origin